Method and system for returning to long term evolution network and mobile switching center

ABSTRACT

Embodiments of the present invention disclose a method, a mobile switching center and a system for returning to a long term evolution network, which may prevent a UE which does not need to return to the LTE network from mistakenly returning to the LTE network. The method includes: receiving a first CSFB indication corresponding to a UE that is sent by a MME after the UE initiates CSFB, wherein the first CSFB indication is used for identifying that the UE needs to return to a LTE network after circuit service of the UE is finished; and sending, according to the first CSFB indication, a second CSFB indication corresponding to the UE to an RNC/BSC when the circuit service of the UE is finished, wherein the second CSFB indication is used for indicating that the RNC/BSC is to notify the UE of returning to the LTE network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2012/076517, filed on Jun. 6, 2012, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to communications, and in particular, to amethod and a system for returning to a long term evolution network and amobile switching center (Mobile Switching Center, MSC).

BACKGROUND

Circuit service (Circuit Service, CS) network is a wireless network forproviding circuit service such as voice call and the like, and coverageof 2G/3G wireless networks such as a GSM, a WCDMA and the like is quiteuniversal. Meanwhile, with development of network technology, packetservice (Packet Service, PS) networks specialized in providing dataservice, such as long term evolution (Long Term Evolution, LTE), systemarchitecture evolution (System Architecture Evolution, SAE), high-speedpacket access (High-Speed Packet Access, HSPA), high-speed packet accessevolution (High-Speed Packet Access Evolution, HSPA+) and so forth, alsohave broad coverage. Therefore, a CS network and a PS network coexist ina current communication network, and an operator may provide circuitservice for a subscriber by using a 2G/3G network or provide dataservice for a subscriber by using an LTE network. A user equipment (UserEquipment, UE) is a multi-mode terminal, and may perform circuit servicein a CS network or perform data service in a PS network according torequirements of a subscriber.

For the moment, an MSC redirects all UEs to the LTE, thereby raising aproblem that a UE which does not need to return to the LTE networkmistakenly returns to the LTE network.

SUMMARY

Embodiments of the present invention provide a method, an MSC and asystem for returning to a long term evolution network, which may preventa UE which does not need to return to the LTE network from mistakenlyreturning to the LTE network.

To achieve the above-mentioned purpose, the embodiments of the presentinvention adopt the following technical solutions.

In one aspect, a method for returning to a long term evolution networkis provided, including:

receiving, by a first mobile switching center (MSC), a first circuitservice fall back (CSFB) indication corresponding to a user equipment(UE) that is sent by a mobility management entity (Mobility ManagementEntity, MME) after the UE initiates CSFB, wherein the first CSFBindication is used for identifying that the UE needs to return to a longterm evolution (LTE) network after circuit service of the UE isfinished; and

sending, according to the first CSFB indication, a second CSFBindication corresponding to the UE to a radio network controller (RadioNetwork Controller, RNC)/base station controller (Base StationController, BSC) corresponding to the UE when the circuit service of theUE is finished, wherein the second CSFB indication is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.

In another aspect, a method for returning to a long term evolutionnetwork is provided, including:

receiving, when a user equipment (UE) is accessed to a second mobileswitching center (MSC) due to linking area updating (LAU), a first CSFBindication corresponding to the UE that is sent by a first MSC, whereinthe first CSFB indication is sent from a mobility management entity(MME) to the first MSC, and is used for identifying that the UE needs toreturn to a long term evolution (LTE) network after circuit service ofthe UE is finished; and

sending, according to the first CSFB indication, a second CSFBindication corresponding to the UE to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE when thecircuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network.

In another aspect, a method for returning to a long term evolutionnetwork is provided, including:

receiving a request message for initiating circuit service fall back(CSFB) by a user equipment (UE); and

sending a first CSFB indication corresponding to the UE to a firstmobile switching center (MSC), wherein the first CSFB indication is usedfor identifying that the UE needs to return to a long term evolution(LTE) network after circuit service of the UE is finished, so that thefirst MSC or a second MSC accessed by the UE due to linking areaupdating (LAU) sends, according to the received first CSFB indication, asecond CSFB indication corresponding to the UE to a radio networkcontroller (RNC)/base station controller (BSC) corresponding to the UEwhen the circuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network, and the second MSC receives the firstCSFB indication sent by the first MSC.

In another aspect, a method for returning to a long term evolutionnetwork is provided, including:

receiving, when circuit service of a user equipment (UE) is finished, anotification of returning to a long term evolution (LTE) network that issent by a radio network controller (RNC)/base station controller (BSC)corresponding to the UE, wherein the notification of returning to theLTE network includes a notification of returning to the LTE network, andthe notification of returning to the LTE network is sent from theRNC/BSC to the UE after the RNC/BSC receives a second CSFB indicationcorresponding to the UE that is sent by a first mobile switching center(MSC) according to a first CSFB indication received from a mobilitymanagement entity (MME); and returning to the LTE network.

In another aspect, a mobile switching center (MSC) is provided,including:

a receiving unit, configured to receive a first circuit service fallback (CSFB) indication corresponding to a user equipment (UE) that issent by a mobility management entity (MME) after the UE initiates CSFB,wherein the first CSFB indication is used for identifying that the UEneeds to return to a long term evolution (LTE) network after circuitservice of the UE is finished; and

a first sending unit, configured to send, according to the first CSFBindication received by the receiving unit, a second CSFB indicationcorresponding to the UE to a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE when the circuit service of theUE is finished, wherein the second CSFB indication is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.

In another aspect, a mobile switching center (MSC) is provided,including:

an acquiring unit, configured to receive, when a user equipment (UE) isaccessed to the MSC due to linking area updating (LAU), a first CSFBindication corresponding to the UE that is sent by another MSC, whereinthe first CSFB indication is sent from a mobility management entity(MME) to the another MSC, and is used for identifying that the UE needsto return to a long term evolution (LTE) network after circuit serviceof the UE is finished; and

a sending unit, configured to send, according to the first CSFBindication received by the acquiring unit, a second CSFB indicationcorresponding to the UE to a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE when the circuit service of theUE is finished, wherein the second CSFB indication is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.

In another aspect, a mobility management entity (MME) is provided,including:

a receiving unit, configured to receive a request message for initiatingcircuit service fall back (CSFB) by a user equipment (UE); and

a sending unit, configured to send a first CSFB indication correspondingto the UE to a mobile switching center (MSC), wherein the first CSFBindication is used for identifying that the UE needs to return to a longterm evolution (LTE) network after circuit service of the UE isfinished, so that the MSC or another MSC accessed by the UE due tolinking area updating (LAU) sends, according to the first CSFBindication, a second CSFB indication corresponding to the UE to a radionetwork controller (RNC)/base station controller (BSC) corresponding tothe UE when the circuit service of the UE is finished, wherein thesecond CSFB indication is used for indicating that the RNC/BSC is tonotify the UE of returning to the LTE network, wherein the another MSCreceives the first CSFB indication sent by the MSC.

In another aspect, a user equipment (UE) is provided, including:

a receiving unit, configured to receive, when circuit service of the UEis finished, a notification of returning to a long term evolution (LTE)network that is sent by a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE, wherein the notification ofreturning to the LTE network includes a notification of returning to theLTE network, and the notification of returning to the LTE network issent from the RNC/BSC to the UE after the RNC/BSC receives a second CSFBindication corresponding to the UE that is sent by a first mobileswitching center (MSC) according to a first CSFB indication receivedfrom a mobility management entity (MME); and

an executing unit, configured to return to the LTE network after thereceiving unit receives the notification of returning to the long termevolution (LTE) network sent by the RNC/BSC.

In another aspect, a system of returning to a long term evolutionnetwork is provided, including a first MSC, an MME, a UE and an RNC/BSCcorresponding to the UE; wherein

the first MSC is configured to receive a first CSFB indicationcorresponding to the UE that is sent by the mobility management entity(MME) after the user equipment (UE) initiates circuit service fall back(CSFB), the first CSFB indication being used for identifying that the UEneeds to return to a long term evolution (LTE) network after circuitservice of the UE is finished; and send, according to the first CSFBindication, a second CSFB indication corresponding to the UE to theradio network controller (RNC)/base station controller (BSC)corresponding to the UE when the circuit service of the UE is finished,the second CSFB indication being used for indicating that the RNC/BSC isto notify the UE of returning to the LTE network;

the MME is configured to receive a request message for initiatingcircuit service fall back (CSFB) by the UE, and send the first CSFBindication corresponding to the UE to the first MSC;

the RNC/BSC is configured to receive the second CSFB indicationcorresponding to the UE that is sent by the first MSC, and notify the UEof returning to the LTE network; and

the UE is configured to initiate a CSFB request to the MME, and receivea notification of returning to the long term evolution (LTE) networksent by the RNC/BSC when the circuit service of the UE is finished.

According to the method, the MSC and the system for returning to the LTEnetwork provided by the embodiments of the present invention, the firstMSC receives the first CSFB indication sent by the MME before a CSFBflow is executed, such that the first MSC may distinguish whether a UEneeds to return to the LTE network after circuit service of the UE isfinished, and thus only a UE with CSFB is notified of returning to theLTE network. Compared with an existing technology in which any UE isinstructed to return to the LTE network after circuit service of the UEis finished, the first MSC may distinguish a UE of which circuit serviceis aroused by CSFB, thereby avoiding a UE which does not need to returnto the LTE network from mistakenly returning to the LTE network.

BRIEF DESCRIPTION OF DRAWINGS

To illustrate the technical solutions in the embodiments of the presentinvention or in the prior art more clearly, a brief introduction on theaccompanying drawings which are needed in the description of theembodiments or the prior art is given below. Apparently, theaccompanying drawings in the description below are merely some of theembodiments of the present invention, based on which other drawings maybe obtained by those of ordinary skill in the art without any creativeeffort.

FIG. 1 is a flow diagram of a method for returning to an LTE network inan embodiment of the present invention;

FIG. 2 is a flow diagram of a method for returning to an LTE network inanother embodiment of the present invention;

FIG. 3 is a flow diagram of a method for returning to an LTE network inanother embodiment of the present invention;

FIG. 4 is a flow diagram of a method for returning to an LTE network inanother embodiment of the present invention;

FIG. 5 is a flow diagram of a method for returning to an LTE network inanother embodiment of the present invention;

FIG. 6 is a flow diagram of a method for returning to an LTE network inanother embodiment of the present invention;

FIG. 7 is a schematic diagram of an arrangement of an MSC in anotherembodiment of the present invention;

FIG. 8 is a schematic diagram of an arrangement of an MSC in anotherembodiment of the present invention;

FIG. 9 is a schematic diagram of an arrangement of an MSC in anotherembodiment of the present invention;

FIG. 10 is a schematic diagram of an arrangement of an MSC in anotherembodiment of the present invention;

FIG. 11 is a schematic diagram of an arrangement of an MME in anotherembodiment of the present invention; and

FIG. 12 is a schematic diagram of an arrangement of a UE in anotherembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The technical solutions in the embodiments of the present invention willbe described clearly and fully hereinafter in conjunction with theaccompanying drawings in the embodiments of the present invention.Obviously, the embodiments described are merely a part, but not all, ofthe embodiments of the present invention. All of other embodiments,obtained by those of ordinary skill in the art based on the embodimentsof the present invention without any creative effort, fall into theprotection scope of the present invention.

For most of UEs, an LTE signal and a 2G/3G signal cannot besimultaneously transceived concerning implementation complexity andcost. For example, when a UE performs data service or is in an idlestate in an LTE network, if the UE wants to initiate or receive circuitservice (including a voice call, a supplementary service, a locatingservice and the like), circuit service fall back (Circuit Service FallBack, CSFB) flow needs to be executed, and a wireless module of the UEfalls back from LTE to 2G/3G, so that the UE completes the circuitservice in a 2G/3G network. After the circuit service is finished(finish of the circuit service is equivalent to releasing a 2G/3Gwireless connection of the UE), a terminal needs to return to the LTEnetwork, so as to continue to perform the data service in the LTE.

At present, since an MSC can not accurately learn whether circuitservices of respective UEs are aroused by CSFB, the MSC redirect all theUEs to the LTE, thereby raising a problem that a UE which does not needto return to the LTE network mistakenly returns to the LTE network.

To solve the above-mentioned technical problem, the present inventionprovides the following technical solutions.

An embodiment of the present invention provides a method for returningto an LTE network. As shown in FIG. 1, the method includes the followingsteps.

101, after a user equipment (UE) initiates circuit service fall back(CSFB), a first mobile switching center (MSC) receives a first CSFBindication corresponding to the UE that is sent by a mobility managemententity (MME), wherein the first CSFB indication is used for identifyingthat the UE needs to return to a long term evolution (LTE) network aftercircuit service of the UE is finished.

The first CSFB indication may be carried in a first CSFB notificationmessage, and the first CSFB notification message carries the first CSFBindication and a UE identification corresponding to the UE (namely theUE which initiates the CSFB). The MME sends the first CSFB indication tothe first MSC, and the first CSFB indication is used for notifying thefirst MSC that, the circuit service to be performed by the UE is arousedby the CSFB, and the UE may be notified of returning to the LTE networkafter the circuit service is finished.

The first CSFB notification message may specifically be a servicerequest message between the MME and the first MSC, such as, for example,an SGs-service request (SGs-service request) message, wherein SGs is aninterface for co-registration between the MME and the MSC, and theSGs-service request message is a service request message transmittedthrough the SGs interface. Or, the first CSFB notification message maybe a customized CSFB notification message, which is obtained by, forexample, expanding a network protocol.

102, when the circuit service of the UE is finished, a second CSFBindication corresponding to the UE is sent to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE according tothe first CSFB indication, wherein the second CSFB indication is usedfor indicating that the RNC/BSC is to notify the UE of returning to theLTE network.

Finish of the circuit service means release of a 2G/3G wirelessconnection of the UE. If the first MSC provides circuit service for theUE, after the circuit service is finished, the first MSC may trigger theRNC/BSC corresponding to the UE to notify the UE of returning to the LTEnetwork. If the UE is accessed to a second MSC after the CSFB isinitiated, the first MSC can not provide circuit service for the UE, andcircuit service is provided to the UE by the second MSC. For example, ina linking area updating (Linking Area Updating, LAU) scenario, the UEmoves and is connected to the second MSC, then the first MSC may sendthe CSFB indication to the second MSC which provides service for the UE,and the second MSC notifies the RNC/BSC corresponding to the UE afterthe circuit service is finished, so that the RNC/BSC notifies the UE ofreturning to the LTE network.

According to the method for returning to the LTE network provided by theembodiment of the present invention, the first MSC receives the firstCSFB indication sent by the MME before a CSFB flow is executed, suchthat the first MSC may distinguish whether the circuit service of the UEis aroused by CSFB, and thus only a UE with CSFB is notified ofreturning to the LTE network. Compared with an existing technology inwhich any UE is instructed to return to the LTE network after circuitservice of the UE is finished, the first MSC may distinguish a UE ofwhich circuit service is aroused by the CSFB, thereby avoiding a UEwhich does not need to return to the LTE network from mistakenlyreturning to the LTE network.

Another embodiment of the present invention provides a method forreturning to an LTE network. As shown in FIG. 2, the method includes thefollowing steps.

201, when a user equipment (UE) is accessed to a second mobile switchingcenter (MSC) due to linking area updating (LAU), a first CSFB indicationcorresponding to the UE, that is sent by a first MSC, is received,wherein the first CSFB indication is sent from a mobility managemententity (MME) to the first MSC, and is used for identifying that the UEneeds to return to a long term evolution (LTE) network after circuitservice of the UE is finished.

If the UE is accessed to the second MSC due to LAU, the second MSC mayprovide circuit service for the UE. In order to learn whether thecircuit service of the UE is aroused by CSFB, the second MSC may acquirethe first CSFB indication from the first MSC. The first CSFB indicationis used for identifying that the UE needs to return to the LTE networkafter the circuit service of the UE is finished.

202, when the circuit service of the UE is finished, a second CSFBindication corresponding to the UE is sent to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE according tothe first CSFB indication, wherein the second CSFB indication is usedfor indicating that the RNC/BSC is to notify the UE of returning to theLTE network.

According to the method for returning to the LTE network provided byanother embodiment of the present invention, since the first MSCreceives the first CSFB indication sent by the MME before a CSFB flow isexecuted, when the second MSC provides circuit service after LAU occursat the UE, the second MSC may receive the first CSFB indication sent bythe first MSC, so that the second MSC may distinguish the UE of whichcircuit service is aroused by the CSFB, and thus a UE which does notneed to return to the LTE network may be prevented from mistakenlyreturning to the LTE network when LAU occurs.

Another embodiment of the present invention provides a method forreturning to an LTE network. As shown in FIG. 3, the method includes thefollowing steps.

301, a UE sends a request message for initiating circuit service fallback (CSFB) to an MME.

The request message for initiating circuit service fall back (CSFB) maybe an extended service request (extended service request) message.

302, the MME sends a first CSFB indication to a first MSC, wherein thefirst CSFB indication is used for identifying that the UE needs toreturn to a long term evolution (LTE) network after circuit service ofthe UE is finished.

303, the first MSC receives the first CSFB indication sent by the MME.

The first CSFB indication may be carried in a first CSFB notificationmessage, and a UE identification and the first CSFB indication, whichare carried in the first CSFB notification message, are acquired. It maybe determined that the circuit service of the UE corresponding to the UEidentification is aroused by CSFB according to the UE identification andthe first CSFB indication.

Further, circuit service of the UE being aroused by the CSFB is intendedto mean that the UE, which is originally in the LTE network, falls backto a CS network to perform circuit service. If the UE is in the CSnetwork before the circuit service is performed, the circuit service isnot aroused by CSFB, the MME will not send the first CSFB indication tothe first MSC, and the UE does not need to return to the LTE networkafter the circuit service is finished.

304, subsequent CSFB flow is executed, so that the UE performs circuitservice in a circuit service (CS) network.

The CS network may be a GSM, a WCDMA, or other wireless communicationnetwork capable of providing circuit service. The circuit service mayinclude a voice call service, a supplementary service, a locatingservice and the like. In the embodiment of the present invention, the UEaccesses the first MSC after the UE falls back to the CS network, andthe first MSC provides circuit service for the UE. It should be notedthat, the first MSC may be selected for the UE by an MME when the UEaccesses the MME, and the MME notifies the UE of relevant identificationinformation of the selected first MSC. When the UE needs to perform theCSFB flow, the UE may be defautly accessed to the first MSC.

305, when the circuit service of the UE is finished, the first MSC sendsa second CSFB indication corresponding to the UE to an RNC/BSCcorresponding to the UE.

It may be appreciated that, if the circuit service of the UE is notaroused by CSFB, the first MSC may not send the second CSFB indicationcorresponding to the UE to the RNC/BSC corresponding to the UE.

An access network control node corresponding to the UE may be a basestation controller (Base Station Controller, BSC), a radio networkcontroller (Radio Network Controller, RNC) or the like. The UE may senda terminal on-hook command to the first MSC, or an MSC at an oppositeend sends a terminal on-hook command to the first MSC, or other commandis utilized to enable the first MSC to judge that the circuit service ofthe UE is finished.

The second CSFB indication may be carried in a second CSFB notificationmessage. For example, the second CSFB notification message may include aUE identification corresponding to the UE which needs to return to theLTE network, the second CSFB indication, other indication of returningto the LTE network or the like, and the second CSFB notification messageis used for notifying the RNC/BSC of notifying the UE of returning tothe LTE network and executing subsequent flow enabling the UE to returnto the LTE network. It may be appreciated that if the first MSC can notdirectly communicate with the RNC/BSC corresponding to the UE, thesecond CSFB indication may be forwarded by an intermediate device.

306, the RNC/BSC corresponding to the UE notifies the UE of returning tothe LTE network.

The RNC/BSC sends a notification of returning to the LTE network to theUE, so as to notify the UE of returning to the LTE network.

307, the UE returns to the LTE network.

After the UE receives the notification of returning to the LTE network,which is sent by the RNC/BSC through step 306, the UE executessubsequent flow for returning to the LTE network. After the UE returnsto the LTE network, the UE may continue to perform data service.

According to the method for returning to the LTE network provided by theembodiment of the present invention, the first MSC receives the firstCSFB indication sent by the MME before a CSFB flow is executed, suchthat the first MSC may distinguish whether a UE needs to return to theLTE network after circuit service of the UE is finished, and thus only aUE with CSFB is notified of returning to the LTE network. Compared withan existing technology in which any UE is instructed to return to theLTE network after circuit service of the UE is finished, the first MSCmay distinguish a UE of which circuit service is aroused by CSFB,thereby avoiding a UE which does not need to return to the LTE networkfrom mistakenly returning to the LTE network.

In another implementation scenario of the embodiment of the presentinvention, a linking area (Linking Area, LA) of a UE is changed and thusthe UE switches to a second MSC. Insteading providing circuit service tothe UE by a first MSC which is selected for the UE by an MME, thecircuit service is provided to the UE by the second MSC. Therefore, theembodiment of the present invention provides a method for returning toan LTE network. As shown in FIG. 4, the method includes the followingsteps.

steps 401-403 are similar to steps 301-303, and a difference lies inthat the first MSC does not provide the circuit service for the UE.Subsequent flow is as follows.

404, the UE accesses a second MSC due to LAU.

The UE is accessed to the second MSC due to LAU. In order to distinguishwhether the circuit service of the UE is aroused by CSFB, the second MSCmay acquire the first CSFB indication corresponding to the UE from thefirst MSC.

405, the second MSC sends a CSFB identification message (sendidentification message) to the first MSC.

As the first MSC is a CS access point selected for the UE by the MME,the MME may notify the UE of identification information of the first MSCbefore a CSFB flow begins. As a result, before the second MSC sends theCSFB identification message to the first MSC, the UE may send an LAUrequest message carrying the identification information of the first MSCto the second MSC, so that the second MSC identifies the first MSCaccording to the identification information of the first MSC and sendsthe CSFB identification message to the first MSC.

406, the first MSC receives the CSFB identification message sent by thesecond MSC.

Specifically, a method for acquiring the CSFB indication by the secondMSC may be as follows: the second MSC sends the CSFB identificationmessage to the first MSC, and if the first MSC receives the first CSFBindication in step 401, a CSFB identification reply message carries thefirst CSFB indication.

Or, a method for acquiring the CSFB indication by the second MSC may beas follows: the CSFB identification message carries an identificationdedicated parameter for indicating that the first MSC is to provide anCSFB indication, and the CSFB identification reply message carries thefirst CSFB indication only when the first MSC obtains the identificationdedicated parameter through parsing. Or, the second MSC may acquire thefirst CSFB indication through other specific message.

407, the first MSC sends a CSFB identification reply message accordingto the first CSFB indication corresponding to the UE that is sent by theMME.

When the first MSC receives the CSFB identification message, the firstMSC may query whether the first CSFB indication sent by the MME isreceived. If the first MSC receives the first CSFB indication sent bythe MME, the first CSFB indication is carried in the CSFB identificationreply message and sent to the second MSC. If the first MSC does notreceive the first CSFB notification message sent by the MME, or thefirst CSFB notification message does not carry the first CSFBindication, the first MSC may reply the CSFB identification messagewithnot carrying the CSFB indication.

Or, after the first MSC receives the CSFB identification message sent bythe second MSC, if the CSFB identification message includes anidentification dedicated parameter, then the first MSC queries whetherthe first CSFB notification message sent by the MME is received andperforms subsequent reply operation of the CSFB identification message.Wherein the identification dedicated parameter is used for indicatingthat the first MSC is to provide the first CSFB indication.

408, subsequent CSFB flow is executed, so that the UE performs circuitservice in a circuit service (CS) network.

It should be noted that, in a CSFB flow, the UE may interact with theMME, the MSC or the RNC/BSC for multiple times, which is not describedin detail in the embodiment of the present invention.

409, when the circuit service of the UE is finished, the second MSCsends a second CSFB indication corresponding to the UE to the RNC/BSCcorresponding to the UE.

The second CSFB indication is used for notifying the RNC/BSC that the UEneeds to return to the LTE network, so that the RNC/BSC notifies the UEof returning to the LTE network.

410, the RNC/BSC corresponding to the UE notifies the UE of returning tothe LTE network.

After the RNC/BSC receives the second CSFB indication corresponding tothe UE that is sent by the second MSC through step 409, the RNC/BSCsends a notification of returning to the LTE network to the UE, so as tonotify the UE of returning to the LTE network.

411, the UE returns to the long term evolution (LTE) network.

After the UE returns to the LTE network, the UE may continue dataservice in the LTE network.

It should be noted that, the second MSC and the first MSC mean that theMME selects the first MSC for the UE and the UE probably switches fromthe first MSC to the second MSC after CSFB. A same MSC device maysimultaneously have functionalities of the first MSC and the second MSC.That is to say, when the UE performs circuit service in a certain MSC,if the MSC is the first MSC selected by the MME, the MSC may receive thefirst CSFB indication sent by the MME; and if the MSC is the second MSCaccessed by the UE due to LAU, the MSC may receive the first CSFBindication corresponding to the UE that is sent from the first MSC. Forspecific description of part of the steps in the embodiment of thepresent invention, reference may be made to corresponding contents inother embodiment, and will not be redundantly described herein in theembodiment of the present invention.

The first MSC receives the first CSFB indication sent by the MME beforea CSFB flow is executed, such that the first MSC may distinguish whethera UE needs to return to the LTE network after circuit service of the UEis finished, and thus only a UE with CSFB is notified of returning tothe LTE network. Compared with an existing technology in which any UE isinstructed to return to the LTE network after circuit service of the UEis finished, the first MSC may distinguish a UE of which circuit serviceis aroused by CSFB, thereby avoiding a UE which does not need to returnto the LTE network from mistakenly returning to the LTE network.

Moreover, when the second MSC provides circuit service after LAU occursat the UE, the second MSC may receive the first CSFB indication sent bythe first MSC, so that the second MSC may distinguish a UE of whichcircuit service is aroused by CSFB, and a UE which does not need toreturn to the LTE network may be prevented from mistakenly returning tothe LTE network when LAU occurs.

Another embodiment of the present invention provides a method forreturning to a long term evolution network, which may be applied to anMME side. As shown in FIG. 5, the method includes the following steps.

501, an MME receives a request message for initiating circuit servicefall back (CSFB) by a UE.

The request message for initiating circuit service fall back (CSFB) maybe an extended service request message, and is used for initiatingcircuit service fall back (CSFB).

There are two scenarios where the UE initiates CSFB. One scenario isthat the UE performs data service or is in an idle state in the LTEnetwork, and wants to initiate a (CS) circuit service. In this case, theUE executes a CSFB flow to switch a wireless module of the UE from LTEto 2G/3G, and initiates circuit service in a 2G/3G network. Such ascenario is referred to as a call initiated by the UE (mobileoriginating call). The other scenario is that the UE performs dataservice or is in an idle state in the LTE network, and the UE receivescircuit service of another UE. In this case, the LTE network notifiesthe UE of arrival of the circuit service, and the UE executes a CSFBflow to switch a wireless module to 2G/3G, and receives the circuitservice in a 2G/3G network. Such a scenario is referred to as anterminating call of the UE (mobile terminating call). In both of the twoscenarios, the UE may initiate CSFB through an extended service requestmessage, which is applicable to different embodiments of the presentinvention.

502, a first CSFB indication corresponding to the UE is sent to a firstMSC, wherein the first CSFB indication is used for identifying that theUE needs to return to a long term evolution (LTE) network after circuitservice of the UE is finished, so that the first MSC or a second MSCaccessed by the UE due to linking area updating (LAU) sends, accordingto the first CSFB indication, a second CSFB indication corresponding tothe UE to a radio network controller (RNC)/base station controller (BSC)corresponding to the UE when the circuit service of the UE is finished,wherein the second CSFB indication is used for indicating that theRNC/BSC is to notify the UE of returning to the LTE network, and thesecond MSC receives the first CSFB indication sent by the first MSC.

The first CSFB indication is carried in a service request messagebetween the MME and the first MSC, such as, for example, an SGs-servicerequest message, or carried in a customized CSFB notification message.

In the embodiment of the present invention, when the UE initiates CSFB,the MME sends the first CSFB indication to the first MSC. On thecontrary, if the UE directly performs circuit service in an MSC, theoperation of sending the first CSFB indication to the first MSC by theMME is not triggered. Therefore, the MSC may not execute relevantoperation of enabling the UE to return to the LTE network after thecircuit service of the UE is finished, and the UE may remain in the CSnetwork. For specific description of part of the steps in the embodimentof the present invention, reference may be made to correspondingcontents in other embodiments, and will not be redundantly describedherein in the embodiment of the present invention.

According to the method for returning to the LTE network provided by theembodiment of the present invention, the first MSC receives the firstCSFB indication sent by the MME before a CSFB flow is executed, suchthat the first MSC may distinguish whether a UE needs to return to theLTE network after circuit service of the UE is finished, and thus only aUE with CSFB is notified of returning to the LTE network. Compared withan existing technology in which any UE is instructed to return to theLTE network after circuit service of the UE is finished, the first MSCmay distinguish a UE of which circuit service is aroused by CSFB,thereby avoiding a UE which does not need to return to the LTE networkfrom mistakenly returning to the LTE network.

Another embodiment of the present invention also provides a method forreturning to a long term evolution network, which may be applied to a UEside. As shown in FIG. 6, the method includes the following steps.

601, when circuit service of a user equipment (UE) is finished, the UEreceives a notification of returning to a long term evolution (LTE)network, which is sent by a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE.

The notification of returning to the LTE network includes a notificationof returning to the LTE network, which is sent from the RNC/BSC to theUE after the RNC/BSC receives a second CSFB indication corresponding tothe UE that is sent by a first mobile switching center (MSC) accordingto a first CSFB indication received from a mobility management entity(MME).

602, the UE returns to the LTE network.

In another application scenario of the embodiment of the presentinvention, the notification of returning to the LTE network furtherincludes a notification of returning to the LTE network sent from theRNC/BSC to the UE after the RNC/BSC receives the second CSFB indicationcorresponding to the UE that is sent by the second MSC according to thefirst CSFB indication received from the first MSC.

According to the method for returning to the LTE network provided by theembodiment of the present invention, the first MSC receives the firstCSFB indication sent by the MME before a CSFB flow is executed, suchthat the first MSC may distinguish whether the circuit service of the UEis aroused by CSFB, and thus only a UE with CSFB is notified ofreturning to the LTE network. Compared with an existing technology inwhich any UE is instructed to return to the LTE network after circuitservice of the UE is finished, the first MSC may distinguish a UE ofwhich circuit service is aroused by the CSFB, thereby avoiding a UEwhich does not need to return to the LTE network from mistakenlyreturning to the LTE network.

Another embodiment of the present invention further provides an MSC,which is used for executing the above-mentioned method for returning tothe LTE network. As shown in FIG. 7, the MSC includes a receiving unit71 and a first sending unit 72.

The receiving unit 71 is configured to receive a first circuit servicefall back (CSFB) indication corresponding to a user equipment (UE) thatis sent by a mobility management entity (MME) after the UE initiatesCSFB, wherein the first CSFB indication is used for identifying that theUE needs to return to a long term evolution (LTE) network after circuitservice of the UE is finished.

The first CSFB indication received by the receiving unit 71 may becarried in a service request message between the MME and the MSC, orcarried in a customized CSFB notification message.

The first sending unit 72 is configured to send, according to the firstCSFB indication received by the receiving unit, a second CSFB indicationcorresponding to the UE to a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE when the circuit service of theUE is finished, wherein the second CSFB indication is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.

Further, the MSC may further include a serving unit 74.

The serving unit 74 is configured to execute subsequent CSFB flow afterthe receiving unit 71 receives the first CSFB indication correspondingto the UE that is sent by the mobility management entity (MME), so thatthe UE performs circuit service in a circuit service (CS) network.

The UE is switched to another MSC due to change of LA, and circuitservice is provided to the UE by the another MSC rather than theabove-mentioned MSC selected for the UE by the MME.

Further, optionally, in another application scenario of the embodimentof the present invention, as shown in FIG. 8, the MSC may furtherinclude a second sending unit 73.

The second sending unit 73 is configured to send the first CSFBindication to another MSC if the UE is accessed to the another MSC dueto linking area updating (LAU), so as for the another MSC to send,according to the first CSFB indication, the second CSFB indicationcorresponding to the UE to the radio network controller (RNC)/basestation controller (BSC) corresponding to the UE when the circuitservice of the UE is finished, and the second CSFB is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.

Further, the second sending unit 73 includes a receiving module 731 anda reply module 732.

The receiving module 731 is configured to receive a CSFB identificationmessage sent by the another MSC.

The reply module 732 is configured to send a CSFB identification replymessage according to the first CSFB indication corresponding to the UEthat is sent by the MME, wherein the CSFB identification reply messagecarries the first CSFB indication.

The CSFB identification message received by the receiving module 731 maycarry an identification dedicated parameter, and the identificationdedicated parameter is used for indicating that the MSC is to providethe first CSFB indication.

The first MSC in the another embodiment of the present inventionmentioned above may be realized by the MSC provided by the presentembodiment; and the second MSC in the another embodiment of the presentinvention mentioned above may be realized by the another MSC provided bythe present embodiment.

Another embodiment of the present invention further provides an MSC. Asshown in FIG. 9, the MSC includes an acquiring unit 81 and a sendingunit 82.

The acquiring unit 81 is configured to receive, when a user equipment(UE) is accessed to the MSC due to linking area updating (LAU), a firstCSFB indication corresponding to the UE that is sent by another MSC,wherein the first CSFB indication is sent from a mobility managemententity (MME) to the another MSC, and is used for identifying that the UEneeds to return to the long term evolution (LTE) network after circuitservice of the UE is finished.

The sending unit 82 is configured to send, according to the first CSFBindication acquired by the acquiring unit 81, a second CSFB indicationcorresponding to the UE to a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE when the circuit service of theUE is finished, wherein the second CSFB indication is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.

Further, as shown in FIG. 10, the acquiring unit 81 may include asending module 811 and a receiving module 812.

The sending module 811 is configured to send a circuit service fall back(CSFB) identification message to the another MSC after the UE isaccessed to the MSC due to linking area updating (LAU).

The receiving module 812 is configured to receive a CSFB identificationreply message sent by the another MSC, wherein the CSFB identificationreply message carries the first CSFB indication.

The first MSC in the another embodiment of the present inventionmentioned above may be realized by the another MSC provided by thepresent embodiment, and the second MSC in the another embodiment of thepresent invention mentioned above may be realized by the MSC provided bythe present embodiment.

Another embodiment of the present invention further provides an MME. Asshown in FIG. 11, the MME includes a receiving unit 91 and a sendingunit 92.

The receiving unit 91 is configured to receive a request message forinitiating circuit service fall back (CSFB) by a user equipment (UE).

The sending unit 92 is configured to send, after the receiving unit 91receives the request message for CSFB, a first CSFB indicationcorresponding to the UE to a mobile switching center (MSC), wherein thefirst CSFB indication is used for identifying that the UE needs toreturn to a long term evolution (LTE) network after circuit service ofthe UE is finished, so that the MSC or another MSC accessed by the UEdue to linking area updating (LAU) sends, according to the first CSFBindication, a second CSFB indication corresponding to the UE to a radionetwork controller (RNC)/base station controller (BSC) corresponding tothe UE when the circuit service of the UE is finished, wherein thesecond CSFB indication is used for indicating that the RNC/BSC is tonotify the UE of returning to the LTE network, and the another MSCreceives the first CSFB indication sent by the MSC.

Before the receiving unit 91 receives the request message for initiatingCSFB sent by the UE, the MME already selects an MSC for the UE and sendsidentification information of the MSC to the UE, so that, when the UEperforms linking area updating (LAU), the identification information ofthe MSC is written into an LAU message and sent to the another MSC.

The first MSC in the another embodiment of the present inventionmentioned above may be realized by the MSC described in the presentembodiment; and the second MSC in the another embodiment of the presentinvention mentioned above may be realized by the another MSC describedin the present embodiment.

Another embodiment of the present invention further provides a UE. Asshown in FIG. 12, the UE includes a receiving unit 1001 and an executingunit 1002.

The receiving unit 1001 is configured to receive, when circuit serviceof the UE is finished, a notification of returning to a long termevolution (LTE) network sent by a radio network controller (RNC)/basestation controller (BSC) corresponding to the UE.

The notification of returning to the LTE network includes a notificationof returning to the LTE network, which is sent from the RNC/BSC to theUE after the RNC/BSC receives a second CSFB indication corresponding tothe UE that is sent by a first mobile switching center (MSC) accordingto a first CSFB indication sent by an MME.

The executing unit 1002 is configured to return to the LTE network afterthe receiving unit 1001 receives the notification of returning to thelong term evolution (LTE) network sent by the RNC/BSC.

Further, optionally, the notification of returning to the LTE networkmay further include a notification of returning to the LTE network sentfrom the RNC/BSC to the UE after the RNC/BSC receives a second CSFBindication sent by a second MSC according to the first CSFB indicationreceived from the first MSC.

An embodiment of the present invention further provides a system forreturning to an LTE network. Reference may be made to an architectureshown in FIG. 3, and the system includes an MSC, an MME, a UE and anRNC/BSC corresponding to the UE.

The MSC is configured to receive a first CSFB indication correspondingto the UE that is sent by the mobility management entity (MME) after theuser equipment (UE) initiates circuit service fall back (CSFB), thefirst CSFB indication being used for identifying that the UE needs toreturn to a long term evolution (LTE) network after circuit service ofthe UE is finished; and send, according to the first CSFB indication, asecond CSFB indication corresponding to the UE to the radio networkcontroller (RNC)/base station controller (BSC) corresponding to the UEwhen the circuit service of the UE is finished, the second CSFBindication being used for indicating that the RNC/BSC is to notify theUE of returning to the LTE network.

The MME is configured to receive an extended service request messagesent by the UE, and send the first CSFB indication corresponding to theUE to the MSC.

The RNC/BSC is configured to receive the second CSFB notificationmessage sent by the MSC, and notify the UE of returning to the LTEnetwork.

The UE is configured to initiate a CSFB request to the MME, receive anotification of returning to the long term evolution (LTE) network sentby the radio network controller RNC/base station controller BSCcorresponding to the UE when the circuit service of the user equipment(UE) is finished, and return to the LTE network.

The notification of returning to the LTE network includes a notificationof returning to the LTE network, which is sent from the RNC/BSC to theUE after the RNC/BSC receives a second CSFB indication corresponding tothe UE that is sent by the mobile switching center (MSC) according to afirst CSFB indication received from the mobility management entity(MME).

The first MSC in the another embodiment of the present inventionmentioned above may be realized by the MSC in the system for returningto the LTE network provided by the present embodiment.

Another embodiment of the present invention further provides a systemfor returning to an LTE network. Reference may be made to thearchitecture shown in FIG. 4. The system includes an MSC, another MSC,an MME, a UE and an RNC/BSC corresponding to the UE.

The MME is configured to receive an extended service request messagesent by the UE, and send a first CSFB notification message to the MSC.The MME is further configured to select, before the extended servicerequest message sent by the UE is received, an MSC for the UE and sendidentification information of the MSC to the UE, so that the UE performsLAU.

The MSC is configured to receive a first CSFB indication sent by themobility management entity (MME).

The another MSC is configured to execute subsequent CSFB flow, so thatthe UE performs circuit service in a circuit service (CS) network. Theanother MSC is further configured to send, after a linking area updating(LAU) request message sent by the UE is received, a circuit service fallback (CSFB) identification message to the MSC, wherein the LAU requestmessage carries identification information of the MSC; receive a CSFBidentification reply message sent by the MSC, wherein the identificationreply message includes the first CSFB indication; and send, when thecircuit service of the UE is finished, a second CSFB indicationcorresponding to the UE to the RNC/BSC corresponding to the UE, whereinthe second CSFB indication is used for indicating that the RNC/BSCcorresponding to the UE is to notify the UE of returning to the longterm evolution (LTE) network. Further, the CSFB identification messagemay carry an identification dedicated parameter for indicating that theMSC is to provide the CSFB indication, and the MSC sends the first CSFBindication to the another MSC after the MSC receives the identificationdedicated parameter.

The RNC/BSC is configured to receive the second CSFB indicationcorresponding to the UE that is sent by the another MSC, and notify theUE of returning to the LTE network. After the UE receives thenotification of returning to the LTE network, the UE executes subsequentoperation of returning to the LTE network, and the UE may continue dataservice after returning to the LTE network.

The UE is configured to initiate a CSFB request to the MME; receive anotification of returning to the long term evolution (LTE) network sentby the radio network controller (RNC)/base station controller (BSC)corresponding to the UE when the circuit service of the user equipment(UE) is finished; and return to the LTE network.

The notification of returning to the LTE network further includes anotification of returning to the LTE network, which is sent from theRNC/BSC to the UE after the RNC/BSC receives the second CSFB indicationcorresponding to the UE that is sent by the another MSC according to thefirst CSFB indication received from the MSC.

The first MSC in the another embodiment of the present inventionmentioned above may be realized by the MSC in the system for returningto the LTE network provided by the present embodiment; and functionalityof the second MSC in the another embodiment of the present inventionmentioned above may be realized by the another MSC in the system forreturning to the LTE network provided by the present embodiment.

It should be noted that, for specific description of part of functionalmodules/units in the MSC, the another MSC, the MME, the UE and in thesystem for returning to the LTE network provided by the embodiment ofthe present invention, reference may be made to description ofcorresponding contents in other embodiments, and will not be redundantlydescribed herein in the embodiment of the present invention.

According to the MSC, the MME, the UE and the system for returning tothe LTE network provided by the embodiment of the present invention, theMSC receives the first CSFB indication sent by the MME before a CSFBflow is executed, such that the MSC may distinguish whether a UE needsto return to LTE network after the circuit service of the UE isfinished, and thus only a UE with CSFB is notified of returning to theLTE network. Compared with an existing technology in which any UE isinstructed to return to the LTE network after circuit service of the UEis finished, the MSC may distinguish a UE of which circuit service isaroused by the CSFB, thereby avoiding a UE which does not need to returnto the LTE network from mistakenly returning to the LTE network.

Moreover, when the another MSC provides circuit service after LAU occursat a UE, the another MSC may receive the first CSFB indication sent bythe MSC, so that the another MSC may distinguish a UE of which circuitservice is aroused by the CSFB, and a UE which does not need to returnto the LTE network may be prevented from mistakenly returning to the LTEnetwork when LAU occurs.

Acts and operations described herein can include the execution ofmicrocoded instructions as well as the use of sequential logic circuitsto transform data or to maintain it at locations in the memory system ofthe computer or in the memory systems of a distributed computingenvironment. The substance of the technical solution of the presentinvention or the part of the present invention making contribution tothe prior art may be embodied in the form of a software product, and thecomputer software product is stored in a readable storage medium, suchas, for example, a soft disk of a computer, a hard disk, an optical diskor the like, which includes multiple instructions enabling one computerdevice (such as a personal computer, a server, a network device or thelike) to execute the methods described in the respective embodiments ofthe present invention. Programs executing on a computer system or beingexecuted by parts of a processor can perform acts and operationsdescribed herein. A “program” is any instruction or set of instructionsthat can execute on a computer, including a process, procedure,function, executable code, dynamic-linked library (DLL), applet, nativeinstruction, engine, thread, or the like. A program, as contemplatedherein, can also include a commercial software application or product,which may itself include several programs. However, while certainelements of the invention can be described in the context of software,that context is not meant to be limiting. Those of skill in the art willappreciate that various acts and operations described herein can beimplemented in hardware.

The foregoing descriptions are merely specific implementation manners ofthe present invention, rather than limiting the protection scope of thepresent invention. Any change or substitution that is readily conceivedfor any one skilled in the art within the technical scope disclosed bythe present invention shall fall into the protection scope of theinvention. Therefore, the protection scope of the present inventionshall be defined by the claims.

What is claimed is:
 1. A method for returning to a long term evolutionnetwork, comprising: receiving, by a first mobile switching center(MSC), a first circuit service fall back (CSFB) indication correspondingto a user equipment (UE) that is sent by a mobility management entity(MME) after the UE initiates CSFB, wherein the first CSFB indication isused for identifying that the UE needs to return to a long termevolution (LTE) network after circuit service of the UE is finished; andsending, according to the first CSFB indication, a second CSFBindication corresponding to the UE to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE when thecircuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network.
 2. The method of claim 1, furthercomprising: sending the first CSFB indication to a second MSC if the UEis accessed to the second MSC due to linking area updating (LAU), so asfor the second MSC to send, according to the first CSFB indication, thesecond CSFB indication corresponding to the UE to the RNC/BSCcorresponding to the UE when the circuit service of the UE is finished,such that the RNC/BSC notifies the UE of returning to the LTE network.3. The method of claim 2, wherein the sending the first CSFB indicationto the second MSC, comprises: receiving a CSFB identification messagesent by the second MSC; and sending a CSFB identification reply messageaccording to the first CSFB indication corresponding to the UE that issent by the MME, wherein the CSFB identification reply message carriesthe first CSFB indication.
 4. The method of claim 3, wherein the CSFBidentification message carries an identification dedicated parameter,and the identification dedicated parameter is used for indicating thatthe first MSC is to provide the first CSFB indication.
 5. The method ofclaim 1, wherein after the first MSC receives the first CSFB indicationcorresponding to the UE that is sent by the MME, the method furthercomprises: executing subsequent CSFB flow, so that the UE performscircuit service in a circuit service (CS) network.
 6. The method ofclaim 1, wherein the first CSFB indication is carried in one of aservice request message between the MME and the first MSC and acustomized CSFB notification message.
 7. A method for returning to along term evolution network, comprising: receiving, when a userequipment (UE) is accessed to a second mobile switching center (MSC) dueto linking area updating (LAU), a first CSFB indication corresponding tothe UE that is sent by a first MSC, wherein the first CSFB indication issent from a mobility management entity (MME) to the first MSC, and isused for identifying that the UE needs to return to a long termevolution (LTE) network after circuit service of the UE is finished; andsending, according to the first CSFB indication, a second CSFBindication corresponding to the UE to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE when thecircuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network.
 8. The method of claim 7, wherein thereceiving a first CSFB indication corresponding to the UE that is sentby a first MSC, comprises: sending a CSFB identification message to thefirst MSC; and receiving a CSFB identification reply message sent by thefirst MSC, wherein the CSFB identification reply message carries thefirst CSFB indication received from the MME by the first MSC.
 9. Amethod for returning to a long term evolution network, comprising:receiving a request message for initiating circuit service fall back(CSFB) by a user equipment (UE); and sending a first CSFB indicationcorresponding to the UE to a first mobile switching center (MSC),wherein the first CSFB indication is used for identifying that the UEneeds to return to a long term evolution (LTE) network after circuitservice of the UE is finished, so that one of the first MSC and a secondMSC accessed by the UE due to linking area updating (LAU) sends,according to the received first CSFB indication, a second CSFBindication corresponding to the UE to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE when thecircuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network, and the second MSC receives the firstCSFB indication sent by the first MSC.
 10. The method of claim 9,wherein the first CSFB indication is carried in one of a service requestmessage between the MME and the first MSC and a customized CSFBnotification message.
 11. A mobile switching center (MSC), comprising: areceiving unit, configured to receive a first circuit service fall back(CSFB) indication corresponding to a user equipment (UE) that is sent bya mobility management entity (MME) after the UE initiates CSFB, whereinthe first CSFB indication is used for identifying that the UE needs toreturn to a long term evolution (LTE) network after circuit service ofthe UE is finished; and a first sending unit, configured to send,according to the first CSFB indication received by the receiving unit, asecond CSFB indication corresponding to the UE to a radio networkcontroller (RNC)/base station controller (BSC) corresponding to the UEwhen the circuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network.
 12. The MSC of claim 11, furthercomprising: a second sending unit, configured to send the first CSFBindication to another MSC if the UE is accessed to the another MSC dueto linking area updating (LAU), so as for the another MSC to send,according to the first CSFB indication, the second CSFB indicationcorresponding to the UE to the RNC/BSC corresponding to the UE when thecircuit service of the UE is finished, such that the RNC/BSC notifiesthe UE of returning to the LTE network.
 13. The MSC of claim 12, whereinthe second sending unit comprises: a receiving module, configured toreceive a CSFB identification message sent by the another MSC; and areply module, configured to send a CSFB identification reply messageaccording to the first CSFB indication received by the receiving unit,wherein the CSFB identification reply message carries the first CSFBindication.
 14. The MSC of claim 13, wherein the CSFB identificationmessage received by the receiving module carries an identificationdedicated parameter, and the identification dedicated parameter is usedfor indicating that the MSC is to provide the first CSFB indication. 15.The MSC of claim 11, further comprising: a serving unit, configured toexecute subsequent CSFB flow after the receiving unit receives the firstCSFB indication corresponding to the UE that is sent by the MME, so thatthe UE performs circuit service in a circuit service (CS) network. 16.The MSC of claim 11, wherein the first CSFB indication received by thereceiving unit is carried in one of a service request message betweenthe MME and the MSC and a customized CSFB notification message.
 17. Amobile switching center (MSC), comprising: an acquiring unit, configuredto receive, when a user equipment (UE) is accessed to the MSC due tolinking area updating (LAU), a first CSFB indication corresponding tothe UE that is sent by another MSC, wherein the first CSFB indication issent from a mobility management entity (MME) to the another MSC, and isused for identifying that the UE needs to return to a long termevolution (LTE) network after circuit service of the UE is finished; anda sending unit, configured to send, according to the first CSFBindication received by the acquiring unit, a second CSFB indicationcorresponding to the UE to a radio network controller (RNC)/base stationcontroller (BSC) corresponding to the UE when the circuit service of theUE is finished, wherein the second CSFB indication is used forindicating that the RNC/BSC is to notify the UE of returning to the LTEnetwork.
 18. The MSC of claim 17, wherein the acquiring unit comprises:a sending module, configured to send a circuit service fall back (CSFB)identification message to the another MSC after the UE is accessed tothe MSC due to LAU; and a receiving module, configured to receive a CSFBidentification reply message that is sent by the another MSC accordingto the first CSFB indication corresponding to the UE, wherein the CSFBidentification reply message carries the first CSFB indication.
 19. Amobility management entity (MME), comprising: a receiving unit,configured to receive a request message for initiating circuit servicefall back (CSFB) by a user equipment (UE); and a sending unit,configured to send, after the receiving unit receives the requestmessage for CSFB, a first CSFB indication corresponding to the UE to amobile switching center (MSC), wherein the first CSFB indication is usedfor identifying that the UE needs to return to a long term evolution(LTE) network after circuit service of the UE is finished, so that oneof the MSC and another MSC accessed by the UE due to linking areaupdating (LAU) sends, according to the first CSFB indication, a secondCSFB indication corresponding to the UE to a radio network controller(RNC)/base station controller (BSC) corresponding to the UE when thecircuit service of the UE is finished, wherein the second CSFBindication is used for indicating that the RNC/BSC is to notify the UEof returning to the LTE network, and the another MSC receives the firstCSFB indication sent by the MSC.
 20. The MME of claim 19, wherein thefirst CSFB indication is carried in one of a service request messagebetween the MME and the MSC and a customized CSFB notification message.